A blumpkuzi is to give somebody a ballcuzi and a blumpkin at the same time. This is a job for two people, it is literally impossible to do with one person. These two people do not include the man who is recieving the blumpkuzi.

Miles: Dude I heard those two girls gave you a blumpkuzi. Which one gave you the blumpkin and which one was doing the ballcuzi?

Dylan: Haha how the fuck am i supposed to know, I was so shitfaced that night.